Processes for the polymerization of olefins are well known in the art. Such processes can be conducted, for example, by introducing an olefinic monomer and other reagents, such as comonomers, chain transfer agents and inert reagents, into a polymerization reactor comprising polyolefin and a catalyst for the polymerization.
A number of different types of catalyst are also known for use in polymerisations, including so-called “Philips” catalysts, Ziegler-Natta catalysts and metallocene catalysts.
Processes for polymerisation, whilst widely operated commercially, can be sensitive to many factors which affect properties of the reaction, such as activity, or the product, such as density and Melt Index. For example, impurities that affect activity can come from the feedstocks, the start-up bed or residual contamination in the reaction loop, but are not easily detected by conventional on-line analysers. Thus, even when there is plenty of past commercial experience with a particular reaction, it is still possible that the particular reaction, when started-up, will not produce the target polymer at the targeted, or expected, productivity. Whilst it is generally possible, once polymer is being produced, to adjust reaction conditions to obtain the desired product properties, overcoming “low activity” can be more complicated. For example, a lower activity than expected may be a sign of reactor contamination, and whilst it may be possible to operate with slightly reduced activity compared to that expected in some cases, in other cases it is necessary to shut-down the reaction and clean the reactor prior to starting up the reaction again.
Further, a reduced activity during start-up may also indicate a build-up of unreacted catalyst. If the reason for the reduced activity is suddenly removed then there results the potential for a sudden “runaway” reaction using the built-up catalyst.